Commission only positions are a very slippery slope.
You can work your butt off for hours at your own expense and until or unless there is an actual sale or event booked and paid for....you don't get anything.
I've been in the insurance industry for years and now almost all the jobs are commission only. No reimbursement for gas or expenses for travel. Many employers are going to "commission only" because it cuts down on their overhead for one, and, they think that it basically forces a person to be a go-getter and bring in business. The downside of that is that people can't afford money out of their own pockets to promote a business and drive all over the place with no income coming in.
There certainly can be lots of days when you literally are working for free. Or, going in the hole to do it.
I guess you have to ask yourself approximately how much catered events go for and what your 10% commission would be.
Use a round number...like $10,000. You know what 10% of that is. How many of those events will you have to book a month just to break even for your expenses, let alone get ahead at all? Can you afford to possibly go months without booking any events?
Are they paying for local advertising to get the word out or just relying on you to do that for them for free?
I could be wrong, but it sounds to me like they want work done, but don't want to pay anything until they have some clients signing on the bottom line and in a new business venture, that's asking a lot of someone.
I hope you get it worked out.
Best of luck to you.